The invention relates to a single mode optical waveguide fiber for both single and multiple wavelength channel high performance telecommunications systems. The inventive waveguide fiber is characterized by low but finite dispersion and low dispersion slope over a wide wavelength range.
A high performance telecommunication system carries high data rates over long distances with no electronic regeneration. For example, rates of 10 Gb/s, or more, over unregenerated distances of three to five hundred kilometers have been achieved. A high performance system may employ high power signal lasers, optical amplifiers for repeaters, or wavelength division multiplexing.
Non-linear optical effects, such as four wave mixing and self phase modulation, can become system limiting effects in these high performance systems.
Four wave mixing can be essentially eliminated by maintaining a non-zero absolute vale of dispersion over the range of wavelengths used for wavelength division multiplexing, thereby preventing phase matching and thus interference between the multiplexed signals. However, the dispersion must not be so high as to limit system bit rate or unrepeatered length. Therefore, best performance is realized when the dispersion is maintained in the range of about 0.50 ps/nm/km to 3.5 ps/nm/km over a pre-selected wavelength range of operation.
In addition, the dispersion must be controlled while maintaining control of other required attributes such as attenuation, waveguide fiber geometry, and mode field diameter. The mode field diameter, in particular must be above a pre-selected lower limit, thereby keeping light power per unit area low enough to avoid self phase modulation.
To provide an optical waveguide having the characteristics required for these sophisticated systems, a variety of refractive index profiles have been modelled and tested. The compound core design, discussed in U.S. Pat. No. 4,715,679, Bhagavatula, offers the flexibility to meet high performance system requirements while maintaining the basic requirements such as low attenuation, narrow geometry tolerances, acceptable bending resistance, and high tensile strength. Furthermore, certain of the compound core designs are relatively easy to manufacture, thereby providing enhanced optical waveguide performance without prohibitive cost increases.